WHO: The "Bullet Cluster," named for its distinctive
shape, is formally known as 1E 0657-56, and is the result of the collision of two enormous clusters of galaxies.

WHAT: The collision that created the Bullet Cluster was one of the most energetic events since the
Big Bang.

WHERE: At a distance of nearly 4 billion light years
from Earth, the Bullet Cluster is located in the constellation
Carina, or the "keel" (bottom of a ship).

WHEN: The speed and shape of the bullet, and
other information from various telescopes suggest
that the smaller cluster passed through the core of
the larger one about 150 million years earlier.

HOW: When these two enormous objects collided,
they did so at speeds of several million
miles an hour. The force of this event was so great
that it wrenched the "normal" matter in the form
of hot gas (seen in pink) away from the dark matter
(blue).

WHY: The separation between the hot gas and the
dark matter in this system is direct evidence that dark
matter does, in fact, exist. The exact nature of dark
matter remains unknown, but it is thought to account
for about 25% of the matter in the Universe.